What type of wiring is most commonly used in residential building circuits?

Non-metallic (NM) sheathed cable is the most commonly used wiring in residential building circuits due to its versatility, ease of installation, and cost-effectiveness. NM cable consists of two or more insulated conductors and a bare ground wire, all housed in a flexible plastic sheath. This design makes it lightweight and easy to handle, which is particularly advantageous in residential settings where wiring often needs to navigate through framing.

Moreover, NM cable is suitable for most indoor residential environments, where it is protected from physical damage, and complies with the National Electrical Code (NEC) requirements for wiring types in typical dwelling units. It also has excellent electrical insulation properties, reducing risks of short circuits and electrical hazards.

While other cable types, such as metal conduit, armored cable, and flexible metallic cable, exist and serve specific purposes or environments, they are generally not as practical for standard residential installations due to factors such as cost, weight, and complexity of installation. Their use may be more common in commercial or industrial applications, or specific residential scenarios where additional protection from physical damage is required.